Ink jet printer and printing method

Abstract

An ink jet printer has a number of ink discharge nozzles, a number of actuators respectively associated with the nozzles and arranged to create pressure waves in the ink to be discharged from the respective nozzles, and a controller arranged to apply drive signals to the actuators in accordance with print instructions for an image to be printed. The drive signals include print pulses causing ink droplets to be ejected from the nozzles at timings when the respective nozzle faces an image part of a print medium, and spitting pulses causing ink droplets to be ejected from the nozzles at timings when the respective nozzle faces a non-image part of the print medium. The drive signals further include pre-fire pulses which have an amplitude below a threshold at which ink droplets are ejected, and the controller is arranged to apply the spitting pulses in the form of combined pulse sequences that each include a number of pre-fire pulses preceding the spitting pulse.

The invention claimed is: 
     
       1. An ink jet printer, comprising:
 a number of ink discharge nozzles; 
 a number of actuators respectively associated with the nozzles and arranged to create pressure waves in the ink to be discharged from the respective nozzles; and 
 a controller arranged to apply drive signals to the actuators in accordance with print instructions for an image to be printed, 
 wherein the drive signals comprise:
 print pulses causing image forming droplets to be ejected from the nozzles at timings when the respective nozzle faces an image part of a print medium; 
 spitting pulses causing spit droplets to be ejected from the nozzles at timings when the respective nozzle faces a non-image part of the print medium; and 
 pre-fire pulses which have an amplitude below a threshold at which ink droplets are ejected, and 
 
 wherein the controller is arranged to apply the spitting pulses in the form of combined pulse sequences that each comprise a number of pre-fire pulses preceding the spitting pulse. 
 
     
     
       2. A printing method for printing with an ink jet printer that has a number of ink discharge nozzles, a number of actuators respectively associated with the nozzles and arranged to create pressure waves in the ink to be discharged from the respective nozzles, the method comprising the steps of:
 applying drive signals to the actuators in accordance with print instructions for an image to be printed, wherein the drive signals comprise:
 print pulses causing image forming droplets to be ejected from the nozzles at timings when the respective nozzle faces an image part of a print medium; 
 spitting pulses causing spit droplets to be ejected from the nozzles at timings when the respective nozzle faces a non-image part of the print medium; and 
 pre-fire pulses which have an amplitude below a threshold at which ink droplets are ejected, wherein the spitting pulses are applied in the form of combined pulse sequences that each comprise a number of pre-fire pulses preceding the spitting pulse. 
 
 
     
     
       3. The method according to  claim 2 , wherein print media sheets are moved past the nozzles one after the other, with gaps being formed between successive sheets, and wherein additional pre-fire pulses are applied in a time period in which said gap moves past the nozzles. 
     
     
       4. The method according to  claim 2 , wherein the volume of a spit droplet is smaller than the volume of an image forming droplet. 
     
     
       5. A computer program product comprising program code on a non-transitory computer-readable medium, which program code, when executed on the controller of the ink jet printer as claimed in  claim 1 , causes the controller to perform a method for printing with an ink jet printer that has a number of ink discharge nozzles, a number of actuators respectively associated with the nozzles and arranged to create pressure waves in the ink to be discharged from the respective nozzles, the method comprising the steps of:
 applying drive signals to the actuators in accordance with print instructions for an image to be printed, wherein the drive signals comprise:
 print pulses causing image forming droplets to be ejected from the nozzles at timings when the respective nozzle faces an image part of a print medium; 
 spitting pulses causing spit droplets to be ejected from the nozzles at timings when the respective nozzle faces a non-image part of the print medium; and 
 pre-fire pulses which have an amplitude below a threshold at which ink droplets are ejected, wherein the spitting pulses are applied in the form of combined pulse sequences that each comprise a number of pre-fire pulses preceding the spitting pulse.